1. Field of the Invention
The present invention relates to a system for aiding a medical practitioner, such as a surgeon, in visualizing anatomical structures during medical procedures and more specifically to a system which allows the practitioner to view, in real time, both internal and external anatomical structures.
2. Discussion of Prior Art
Presently, during surgery and other medical procedures such as endoscopy, biopsy and implantation, physicians view several static radiographic views of the patient in the operating room. Typically these are transparent film renderings of magnetic resonance (MR), computed tomography (CT), conventional X-ray images or ultrasound images. Since these images are two dimensional static images, the physicians must determine the actual three-dimensional (3D) location and shape of desired internal structures within the patient from the 2D images which they are viewing. The surgeon conceptually constructs a 3D model of the internal structures and correlates these internal structures with visible external structures of the patient where they must cut. This is often difficult because the scale and the orientation of the 2D image may differ from what the surgeon is seeing, and the surgeon may not be able to view both the patient and the medical diagnostic images simultaneously.
Another technique employed in localization of internal structures during surgery is known as stereotactic surgery as described in "Interactive Stereotactic Surgical System for the Removal of Intracranial Tumors Utilizing the CO.sub.2 Laser and CT-Derived Database" by B. A. Kall, P. J. Kelly, and S. J. Goerss, IEEE Transactions on Biomedical Engineering, vol. BME-32, no. 2, pp 112-116, 1985; and "Comprehensive Computer-Assisted Data Collection Treatment Planning and Interactive Surgery" by B. A. Kall, P. J Kelly, and S. J. Goerss, Medical Imaging, vol. 767 pp. 509-514, 1987. With this approach, a rigid mechanical frame is attached to the patient before a CT or MR procedure. The frame and its landmarks can be seen in the resulting images. Mechanisms on the frame position a probe at specific location within the image. The disadvantages of this approach are that the frame limits access to the patient, and the images are static images which do not follow the patient if he moves during surgery.
A third technique used for localization of internal structures is described in "A Frameless Stereotaxic Operating Microscope for Neurosurgery" by E. M. Friets, J. W. Strohbehn, J. F. Hatch, and D. W. Roberts, IEEE Transactions on Biomedical Engineering, vol. 36., no. 6, pp 608-617, June 1989.
Three dimensional models of anatomical structures can be created from data of different medical imaging modalities as described in the application Ser. No. 07/812,384 listed above in the "CROSS REFERENCE TO RELATED APPLICATIONS". These applications describe creating and manipulating models of internal structures of patients and providing images of selected structures at desired orientations to an operator. These allow visualization of internal structures as solid models.
Currently there is a need for a system to aid physicians in surgery and other medical procedures which interactively displays computer generated representations of internal structures in correct relation with external structures of the patient, and permits visualization of actual and hypothetical paths of invasive devices.